Scrubber Installation Without Dry Docking
By Uwe Aschemeier and Kevin Peters
The year 2020, and with it the Sulphur regulation for the use of heavy Sulphur fuel oil, is approaching fast. Starting January 2020, it will be illegal to run a ship using fuel containing more than 0.5% Sulphur without the operation of a scrubber, an exhaust cleaning gas system. 
Scrubber systems are a diverse group of air pollution control devices that can be used to remove some particulates and/or gases from industrial exhaust streams. Traditionally, the term “scrubber” has referred to pollution control devices that use liquid to wash unwanted pollutants from a gas stream. Scrubbers are one of the primary devices that control gaseous emissions, especially acid gases. 
Subsea Global Solutions (SGS), an underwater ship repair and maintenance specialist headquartered in Miami, FL, USA and with offices around the world, has installed scrubber systems in cruise vessels since 2014, without taking the vessel out of the water or interruption its itinerary.
SGS has performed installations of sea chests and overboard discharge pipes together with several scrubber manufacturers. SGS involvement ranges from the installation of the sea chests, installing overboard discharge pipes, cutting the hull openings for the sea chests and installing grates into the sea chest openings. SGS provides mainly support from the underwater side but was also involved with welding project related to scrubber systems on the inside of vessels. Sea chest design varied from conventional box designs to innovative pipe designs with diameter in excess of 1000 mm.
Sea chest for scrubber system installed on a cruise ship
3 DN 400 overboard discharge pipes installed
during regular port stops
The first scrubber installation project SGS was involved with was in 2014. This project required the manufacturing and installation of the sea chest and the new installation of 3 DN400 overboard discharge pipes. Preparation work was always performed during sea days, while cutting the hull penetrations and welding against the hull was performed during regular port stops. Since then, SGS has been involved with installation of more than 20 scrubber systems on cruise vessels.
To be more efficient, SGS developed a heat barrier system, allowing welding to be performed from the inside of the vessel against the hull. The heat barrier is installed by divers from the water side over the future weld zones. Due to its geometry and profile, the heat barrier can stay on the hull during sea days, which allows welding to be performed immediately after the vessel enters the port.
Once the inside crew completes the installation of the sea chest, SGS divers can be deployed to cut open the hull in way of the sea chest, followed by the installation of the sea chest gratings. The cutting of the sea chest openings may be performed by mechanical means with a specifically designed track saw, thermal cutting with underwater plasma or PVL torch, or with an exothermic process.
Mechanical cutting of hull opening with track saw
Exothermic cutting process
Hull opening cut underwater
Sea chest gratings installed, and corrosion protection applied
SGS has its own welding department, headed by a full-time employed welding engineer. Welding procedures for underwater wet welding and top site welding are in place with major classification societies, like ABS, DNV GL, LR. SGS is currently the only company worldwide, that has a workshop approval from DNV GL for underwater wet welding.
SGS also has approvals to perform permanent underwater wet weld repairs and installations from ABS and DNV GL. These repair and installations may be considered permanent on a case by case approval.
 IMO 2020 Report, March 2018